1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to a method for making a hard socket or a liner by thermoforming.
2. Description of the Prior Art
Some amputees wear socks on their residual limb to provide cushioning between the residual limb and the surface of a hard socket. However, socks cannot provide an airtight seal between the residual limb and the socket. As a result, various means are employed to prevent relative motion between the residual limb and the socket, but such means are largely inadequate.
Accordingly, inventors in the prosthetics industry have developed various rubber-like cushioning means that are adapted to be worn like socks over the residual limb.
Such cushioning means provide an airtight seal around the residual limb. This enables creation of a vacuum in the unoccupied part of the hard socket, i.e., in the lowermost end of the socket below the residual limb. The vacuum substantially prevents relative movement between the residual limb and the socket.
Most rubber-like liners are unacceptable, however, because they are skin-unfriendly and have other unwanted side effects. Urethane, for example, provides the desired cushioning effect but can irritate the skin and create odors.
Silicone RTV has become the material of choice for custom liners. A mold is made that duplicates the geometry of the patient""s stump and liquid RTV silicone is poured into the mold. The mold is opened after twenty four hours and the custom silicone liner is retrieved.
There are several drawbacks to this process. First, it requires the mixing of silicone. Second, it requires the making of a mold. Moreover, the process takes more than a day to complete.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how a custom liner could be made in the absence of silicone mixing, mold-making, and the like.
The longstanding but heretofore unfulfilled need for an improved method for making custom liners is now met by a new, useful, and nonobvious invention. The heart of the invention is its provision of a thermoformable prosthetic liner. The novel method of making a thermoformable tubular liner for use in a prosthetic appliance includes the steps of preparing a negative cast from a patient""s residual limb, preparing a positive cast from the negative cast, and placing a thermoformable tubular liner over the positive cast.
The positive cast and the thermoformable tubular liner are then heated in an oven for a predetermined amount of time, such as thirty minutes, at a predetermined temperature such as about ninety to one hundred degrees Celsius. The cast and thermoformable tubular liner are removed from the oven and allowed to cool to room temperature. The thermoformable tubular liner is then removed from the cast. An interior surface of the thermoformable tubular liner will now be observed to conform to the shape of the positive cast.
A procedure that produces the most consistent results includes the steps of preheating the positive cast, placing the thermoformable liner over the heated cast, placing both the positive cast and the thermoformable liner in the oven, and removing both items from the oven and letting them cool to room temperature.
A faster procedure includes the steps of preheating the thermoformable liner, placing the thermoformable liner over the positive cast, and letting both items cool to room temperature.
The thermoformable tubular liner exhibits elasticity when cooled to room temperature. Accordingly, it returns to its pre-stretched size and shape when stretched and released at room temperature.
The thermoformable tubular liner is adapted to be stretched and fitted over a residual limb. Due to its elasticity, it remains on the residual limb even as the residual limb shrinks during the day.
The positive cast may also be preheated in the oven for a predetermined amount of time such as two to three hours at a predetermined temperature such as about ninety to one hundred degrees Celsius prior to said step of placing the thermoformable tubular liner over the positive cast.
The thermoformable tubular is formulated by mixing triblock copolymers of the styrene, ethylene styrene type with mineral oils at a predetermined concentration. The predetermined concentration is about 200 to 400 parts of mineral oil per 100 parts of polymer.
A fabric may also be applied in overlying relation to an exterior surface of the liner. When a fabric is applied, the step of applying the fabric is performed after the step of placing the thermoformable tubular liner over the positive cast and prior to the step of heating the positive cast and thermoformable tubular liner in the oven.
A general object of the invention is to provide a method for making a custom prosthetic liner by a thermoforming process.
A more specific object is to provide a method for making a custom prosthetic liner where the method requires no silicone mixing and no mold-making.
Another very important object is to provide a thermoformable liner that acquires a new geometry upon being heating in an oven and cooled to room temperature, and which returns to that new geometry upon being stretched and released at room temperature so that it may be worn on a residual limb all day without becoming loose if the residual limb shrinks during the day.
It is also an object of this invention to provide a method for making a thermoformable liner that is easy and economical to follow and that results in high quality liners.
Another object is to provide a thermoformable liner having elasticity so that it may be turned inside out to facilitate putting it on and taking it off.
Yet another object is to provide a thermoformable liner exhibiting elasticity so that it can be used with residual limbs having irregular geometries.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.